The present invention relates generally to a reactive ionized cluster beam deposition method and an apparatus thereof, and more particularly, to a method of and an apparatus for deposition-forming a high quality thin film on the surface of, e.g., a plastic film or the like serving as a substrate.
A technique of deposition-forming a thin film of a metal on a surface of, e.g., a plastic film, etc. is disclosed in, e.g., Japanese Patent Laid-Open Publication No. 52-10869. The conventional thin film forming method disclosed in this Patent Laid-Open Publication basically involves the following steps. A deposition substance is vaporized in a closed type crucible. The vaporized deposition substances are injected from injection nozzles into a vacuum region whose pressure is equal to or less than at least 1/100 of a vapor pressure in the crucible as well as being equal to or smaller than approximately 10.sup.-2 Torr. At the same time, the injected deposition substance bombards the surface of the substrate. The injection speed during the injection is changed, thus controlling a hyperfine structure during the formation of the thin film.
Further, for obtaining a ceramic thin film of a metal oxide or a metal nitride, there exists a reactive ionized cluster beam deposition method requiring an introduction of a reactive gas in addition to the above-mentioned ionized cluster beam method. By the way, according to the ordinary reactive ionized cluster beam (R-ICB) method, the degree of vacuum within the vacuum region is on the order of 2.times.10.sup.-4 .about.5.times.10.sup.-4 Torr. Reaction is induced by supplying sufficient reactive gas in the vicinity of the injection nozzles in the crucible to maintain this degree of vacuum.
According to the conventional reactive ionized cluster beam deposition method, however, an advancement of 10.about.100 cm is required for causing a collision and reaction between the deposition substance and the reactive gas atoms under a degree of vacuum of .times.10.sup.-4. This is based on the following formula obtained approximately from a mean free path theory when the distance from the vaporizing source to the substrate is set to, e.g., about 50 cm. EQU .lambda..apprxeq.10.sup.-2 /Pr
where .lambda. is the mean free path (cm), and Pr is the pressure (Torr). The complete reaction is therefore hard to obtain in the setting described above.
Then, if the reactive gas concentration is enhanced to obtain such a degree of vacuum on the order of .times.10.sup.-3 Torr that the collision advancing distance needed for a sufficient advancement of reaction is 10 cm or less, a glow discharge is produced this time due to the reactive gas in an electron emitter for ionization. This results in a decay of clusters (vaporized atoms or molecules when a deposition substance is vaporized turns into a massive body like a cluster of grapes) due to plasma. The characteristics inherent in the ionized cluster beams are lost, and, at the same time, there arises a problem in terms of degradation of the heating crucible and electrodes derived from the reaction with the reactive gas.
As described above, the conventional reactive ionized cluster beam deposition method presents the following drawbacks. If the necessary gas concentration in the reactive portion is maintained, i.e., if the reactive gas concentration is maintained enough to permit a sufficient advancement of the reaction of the deposition substance with the reaction gas, the heating crucible, the ionizing unit and an acceleration electrode are corroded by the reactive gas. Also, decay of the clusters is caused by the plasma in the electron emitter due to the reactive gas.
Accordingly, it is a primary object of the present invention, which has been devised to obviate the problems peculiar to the prior art, to provide a reactive ionized cluster beam deposition method and an apparatus for forming a deposited film exhibiting an excellent property on the surface of a substrate by the same method.
It is another object of the present invention to prevent a caused-by-reactive-gas degradation of the acceleration electrode when forming a deposited film on the substrate surface by the reactive ionized cluster beam deposition method.
It is still another object of the present invention to prevent a decay of clusters due to the plasma in an electron emitter when forming a deposited film on the substrate surface by the reactive ionized cluster beam deposition method and to maintain a necessary gas concentration in a reactive portion.
It is a further object of the present invention to form a deposited film having a good crystallinity on the substrate surface by the reactive ionized cluster beam deposition method.
It is a still further object of the present invention to provide a film formed with a deposited film which is excellent in terms of a water vaporproof performance and an oxygen barrier performance by the reactive ionized cluster beam deposition method.